Currently there is no such scanning system that is specially defined for inspecting aircrafts. Among the existing security inspection systems that use X-rays or Gamma-rays, only scanning systems that base on the backscatter technology can be used to scan aircrafts. The backscatter technology is to place a ray source and a detector at a same side of an object to be inspected, so that X-rays or Gamma-rays emitted from the ray source reach the object to be inspected, with some particles absorbed by the object to be inspected, while particles that have not been absorbed scatter at the object. Scattered particles transmit through the object to be inspected if the scattering angle is smaller than 90 degrees; while scattered particles are reflected from the incidence side if the scattering angle is larger than 90 degrees. The backscatter principle is to place a ray source and a detector at a same side of an object to be inspected and to detect back scattered particles that are scattered with a scattering angle larger than 90 degrees.
The backscatter based products occupy less area and can be used flexibly. Such scanning systems, however, are not designed dedicatedly for aircraft inspection, and thus have some defects if they are used in aircraft inspection. The backscatter scanning systems have rays of a low energy that cannot penetrate a wing and a fuselage to perform a complete and thorough inspection. In the case that the object is of a low Z material at the portion close to the location where the ray source is located, the rays are scattered with a larger angle at the low Z material, and a lot of particles are reflected and cannot penetrate into the interior of the object to be inspected, and thus a thorough inspection cannot be done. When it comes to an aircraft inspection, the backscatter based products typically is on a mobile on-board platform, and cannot inspect all the portions of an aircraft, e.g., the portions that are far away from the ground (such as a wing) or too close to the ground (such as bottom of a business aircraft). Furthermore, the scanning efficiency of the on-board backscatter scanning systems is low since they need to move along the fuselage and the lateral wings during the scanning of an aircraft.